We propose to study protein metabolism in the preimplantation mouse embryo. Very little is known about metabolism in the mammalian embryo between ovulation and implantation, and the studies planned would provide fundamental information essential to understanding development during this initial period. Two specific areas will be investigated. First, we plan to determine the specific activity of radioactive leucine in the intracellular pool of amino acids of the embryo. This information plus leucine incorporation rates will allow us to calculate for the first time in any mammalian embryo the protein synthetic rate at successive developmental stages. This should tell us about the total translational activity of the embryo. Second, we plan to determine changes which occur in the types of and synthesis of specific proteins during the preimplantation period. We are particularly interested in identifying proteins in which there may be dramatic or large changes during the period. We plan to use proteins for which there is a significant measurable synthesis to determine the half-life of messenger RNA's in the mouse embryo. This should tell us about specific translational activity of the embryo. The major techniques we will use are super-ovulation, mammalian embryo culture, thin layer chromatography, and acrylamide gel electrophoresis.